Cast refractory products



v.metals.

Patented Feb. 25, 1947 i .21 I Theodore Estes Field LouisvilleQKy;assignor to 1 1Corhart Refractories Company, Louisville, Ky.,

. a corporationof, Delaware The tremendous increase closea novel heatcastmrefractory' which has provento be especiallyserviceable' for suchuses.

By heat cast is meant the complete meltingof the ingredients as forexample .wlththe techniques .disclosedlin U. SLPatent-#1,615;-'750to-Fulcher and shaping intothe desired form by castin into molds andsolidifying.

Heat cast refractories of this disclosure consist of well developedinterlocking crystal phases with an amorphous matrixof' much lowersoftening point whichtakes the place of both the fluxing bond and theporosity of the; usual. burnt refracin production of'magn'esium anditsalloys has emphasized the unsatisfactory performance ofpresentlyavailable refra'cv to'ries for melting and containing themolten It is an object :of this inventionto dis- 'flvr'a mg. ApplicationApril 10, 1945, Serial No. 587,512

" sciai sr "(cries-'57 j first atjzroo 'c.;' I obtained melting atstemperature off1850, C. with as little as zirconia added and with 1%ZrOa i men N given below,

the casting temperature was reduced to 1770 C. This'is in contrast tothe addition of AlaQs to spinel where a 31% substitution-still gives amelting temperature M20609 0, in the'pr'esence of 5% SiOz. I have alsofound that .thetendency of castings containing MgO to show internal'g'aspockets ,is greatly reduced as zroz is increased,

possibly because'of the decreased temperature of casting. r To preservethe benefitof an interlocking crystal'network of at least twophases, andto keep ,fer to keep ZrOz between 10 and 60%,. Mg0 between 7 and 2 5 andA1203 between 30 and 8 0%. f

tory. Magnesium is an extremely reactive metal and I have found theelimination of porosity a distinct advantage since it confines theattack to the out i s rface ng, i si er-t e; etractprr a tic a dest ctie Pene ation and reaction since his apt to take place with an increasein volume. I have found that the heat cast refractory, particularly ofmore than one crystal phase, has another distinct advantage in that thecrystals interlock to give a skeleton network which is strongly coherentin itself and is not dependent upon a fluxing bond to hold it together.Thus even though the amorphous matrix is the weakest link in resistanceto attack by the magnesium, its eventual dissolution does not causesloughing off of liberated crystals as with burnt refractories.

The chemical attack by magnesium results from reduction of the oxides ofthe refractory to metal and simultaneous oxidation of the magnesium tomagnesium oxide. Refractory oxides-with the exception of magnesium oxideitself are all subject to such attack. I have discovered however thatwell developed crystals Of'ZIOz and of A1203 which the melting pointswithin commercial limits I pre- Examples of such compositions which Ihave made by melting pure oxides are shown in Table'I.

Table I- a Chemical compositions Calculated phases Melt V ZrQz MgO A120:Spinel Oorundum ZrO;

10 70 35 45 2o 30 20 50 70 0 30 30 10 6O 35 '35 30 40 17 43 60 0 40 4010 50 35 V 40 1 50 10 40 35 15 50 60 10 5 60 Pure ZrOz is very expensiveat present and I therefore prefer (for commercial refractories) to makeuse of a high grade baddeleyite ore as source of ZIOz, the primaryimpurities being a, small amount of SiOz and some iron oxide which is Vlargely reduced out by the carbon electrodes durcan be produced in aheat cast refractory are relatively slowly attacked despite the readyreducibility of these oxides reported in th literature.

Since magnesium oxide is theoretically not reduced at all however, Iprefer to usethe A1203 in combination with MgO as spinel (AlzOs/MgO is2.54) which I have found can be done without raising the melting pointexcessively. In its broadest aspects therefore, my novel heat castrefractory contains well developed Zl'Oz and MgO.A12O3 crystals with orwithout additional corundum crystals.

I have found that the addition of ZrOs to spinel materially increasesthe ease of melting andcasting. Thus while spinel with 5% SiO: presenting melting of the batch. Calcined magnesite may be used as source ofMgO and I prefer tosupply A1203 as the refined product used inelectrolytic manufacture of aluminum although it is within the claims ofthis invention to use less refined materials such as high grade bauxiteor aluminous byproducts.

When the cheaper commercial materials are used,'the various impuritiesconcentrate in the amorphous matrix. Tests have shown that the SiOz insuch matrices is readily reduced bythe molten magnesium and it istherefore highly desirable to keep this ingredient low by using highgrade raw materials. The inclusion of 5% SiO-z is permissible but adecrease in resistance is observable with 10% SiOz. The cracking ofsmall castings is apt to-occur if S102 is not kept above 11% but I havefound. that SiOz can be safely lowered on larger castings and even smallcastings can be obtained at low S102 if small per- 7 centages of K20 orNazO are also included. 'Ex- 'amples of batch compositions withcommercial raw materials which I have cast into refractory blocks areshown in Table II;

Table II Since these compositions are completely melted before castingit is obvious that any raw materials which in .combination will yieldadesire'd chemical analysis can be used. In general the materialsresistance to attack.

By fprincipally in'the' following claims I mean "over 95% of the totalcomposition. v I WhatI claimis:

1. A heat castirefr'actorycontainingmagnesi- "um 'spinel composed of,zirconia, magnesia and alumina in which the zirconia isgbetween 10%, and60%, the magnesia-is 'over 7% and the ratio of alurnina to magnesia isover 2.5 by weight, the

total of said ingredients being atleast 95%.

' the zirconia is between l% and 60% the magnesia is over'7%, the silicais under and the are selectedjwith view toward minimizing the impuritieswithout adding too greatly to the cost since the purest compositionshave the greatest by chemical analysis. c I V i '7. A *heat'castrefractory composed principally 3. A heat cast refractory composedprincipally of crystalline zirconia. and magnesiumspinel in an amorphousmatrix and in which the ZrOz lies ratio of alumina to magnesia is over2.5 by weight. "6. A heat cast refractory composed principally ofzirconia; magnesia; alumina and silica in which the ratio of alumina tomagnesia is over 2.5 by 7 weight and in which ZrOz lies between 10% and60%," MgO between 7%;and A1203 between and 80% and SiOzbetween 0% and10% of crystalline'zirconia and magnesium spinel in asiliceous. matrixand in which the ZrOz lies between 10% and %v and'the SiOais less than10%.by chemical analysis.

8. A heat cast refractory composed principally of crystalline -zirconia,"magnesium spinel and I corundum in a siliceous matrixvand in which theZr02 lies between 10 and. 60% andlthe SiOzis QIGSS than 10% by chemicalanalysis.

. "13 24A heat cast refractory containing ,magnesium' spinelcomposedprincipally of ,zirconia, f'magnesia and aluminain which the-ratio f aluminato magnesia is over'2;5 by weight and in,

. which ZrOz lies between 10 and 60%., MgO bewtween'7% and-25%.and-AlzO3 between'30% and by chemical analysis. a j

THEODORE ESTES I I 3 'RE'FER'EnEs crrED, The following references arefile of this patent:'

I UNITED STATES PATENTS c Number I V 2,271, 69 Fulcher et'a1;; Jan. 27,1942 of record in the

